A patient with necrobiotic xanthogranuloma presenting with an anterior mediastinal mass, plasma cell dyscrasia, and a lymphoproliferative disorder.

Necrobiotic xanthogranuloma (NXG) is a rare systemic disease primarily associated with cutaneous plaques; these plaques can manifest anywhere, but most commonly affect the face and periorbital regions. It has a distinct histopathology with extensive necrobiosis and infiltrates of inflammatory cells. Patients with NXG are often found to have paraproteinemia or hematologic disorders, including multiple myeloma or lymphoproliferative diseases. We describe a case of NXG in a patient without characteristic skin lesions, who was diagnosed after a biopsy of an anterior mediastinal mass. This case is also significant because the patient’s bone marrow biopsy showed simultaneous lymphoproliferative and plasma cell disorders, which, to our knowledge, have not been reported in previous literature.